Improve Elasticsearch setup

What does this Merge Request do and why?

Previously if your .cache directory had a file like .elasticsearch_7.16.1_installed, gdk reconfigure would not download anything even if the elasticsearch directory were empty.

Instead of relying on this marker file, we can look for the existence of the version-specific JAR library.

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.